1. Field of the Invention
This invention relates to a fitting structure for a control valve for controlling a discharge capacity in a variable capacity compressor used for a car air conditioner, for example.
2. Description of the Related Art
The following construction is known for a variable capacity compressor (hereinafter called merely the "compressor") of the kind described above. A crank chamber is defined and partitioned inside a housing, and a drive shaft is rotatably supported by the housing in such a fashion as to cross, transversely, the crank chamber. A swash plate is supported by the drive shaft through a rotary support member inside the crank chamber in such a fashion as to be capable of integrally rotating and rocking. A plurality of pistons are engaged with to the outer peripheral portion of the swash plate. Cylinder bores are formed in a cylinder block, that constitutes a part of the housing, equiangularly arranged around the drive shaft. The head of each piston is fitted into each cylinder bore and is allowed to reciprocate.
When the drive shaft is driven for rotation by driving force transmitted thereto from an external driving source such as a car engine through a belt, or the like, the swash plate is rotated through the rotary support. The rotary motion of this swash plate is converted to the reciprocating motion of each piston. In consequence, a series of compression cycles such as suction of a refrigerant gas into the cylinder bores, compression of the refrigerant gas so sucked and discharge of the compressed refrigerant gas from the cylinder bores are repeated.
In the compressor described above, a discharge pressure region, in which the compressed refrigerant gas stays temporarily, and the crank chamber are connected through an supply passage having a control valve. The control valve is fitted into a fitting hole formed in a rear housing that constitutes a part of the housing of the compressor. This control valve plays the roles of changing an open area in the supply passage and regulating the feeding amount of the high-pressure discharge refrigerant gas into the crank chamber. When the feeding amount of the discharge refrigerant gas is adjusted, the internal pressure of the crank chamber is varied, and the pressure difference between the pressure of the crank chamber piston and the pressure of the cylinder bores through the piston is varied, too. As the pressure difference is varied, the tilt angle of the swash plate is varied, and the stroke of each piston, that is, the discharge capacity, is regulated.
The control valve shown in FIG. 7 is known as a control valve 200 of this kind. The control valve 200 includes a valve body 202 for opening and closing the supply passage 201 described above, an electromagnetic driving portion 203 for changing the load applied to the valve body 202 in accordance with an input current value, and a pressure-sensitive mechanism 205 for changing the load applied to the valve body 202 in accordance with the pressure of the suction pressure region of the compressor. In this control valve, the overall force of the impressed load from the pressure-sensitive mechanism 205 and the impressed load from the electromagnetic driving portion 203 operates the valve body 202, and the open area of the supply passage 201 is decided.
Gas chambers such as a valve chest 207 for storing the valve body 202 and a pressure-sensitive chamber 208 for storing the pressure-sensitive mechanism 205 are defined and partitioned inside the valve housing 206 of the control valve 200. A plurality of step portions 209a to 209c are defined in the valve housing 206. A pressure-sensitive hole 210 that communicates with the pressure-sensitive chamber 208 is open to the first step portion 209a. A valve port 211 that can be connected and disconnected to the valve chest 207 by the valve body 202 is open to the second step portion 209b. An inlet port 212 that communicates with the valve chest 207 is open to the third step portion 209c.
Each of these step portions 209a to 209c is partitioned hermetically by an O-ring 214 while the control valve 200 is fitted to the fitting hole 213 of the compressor. This is because different pressures are guided to the pressure-sensitive hole 210, the valve port 211 and the inlet port 212, respectively.
A taper surface 216 the diameter of which decreases progressively towards the bottom of the fitting hole 213 is formed in the fitting hole 213 in such a fashion as to correspond to a holding portion 215 of the O-ring 214 as shown in FIGS. 5B and 7. As the O-ring 214 passes over the taper surface 216 during the fitting operation of the control valve, it is compressed in a predetermined quantity.
Incidentally, the compressor is mounted in the proximity of the engine inside the car engine room. The mounting space of the compressor inside the engine room is limited, and there has been a strong requirement for reducing the size of the compressor, particularly the requirement for reducing its projecting distance from the outer periphery in the diametric direction of the housing 217.
In the compressor having the conventional construction described above, its control valve 200 includes the electromagnetic driving portion 203 and the pressure-sensitive mechanism 205. Therefore, it is elongated in the axial direction. As indicated by two-dot-chain line in FIG. 3, the control valve 200 is fitted while its proximal end portion protrudes from the outer periphery of the housing 217 of the compressor. When this protruding distance is great, the control valve 200 interferes with the car engine or other auxiliary machinery, and mountability of the compressor to the car is poor.
To cope with this problem, the full length of the control valve 200 in the axial direction may be reduced. In this case, the reduction of the length in the axial direction is limited because the electromagnetic driving portion 203 and the pressure-sensitive mechanism 205 have to apply predetermined impressed loads to the valve body 202 inside the control valve 200. In other words, if the length of electromagnetic driving portion 203 and the pressure-sensitive mechanism 205 are greatly decreased in the axial direction, the predetermined impressed loads are likely to be insufficient, and the regulation capability of the valve body 202 of adjusting the open area to the supply passage 201 may drop. In consequence, stability of discharge capacity control in the compressor may drop.
Therefore, the length in the axial direction must be reduced at the intermediate portion between the electromagnetic driving portion 203 and the pressure-sensitive mechanism 205 in the valve housings 206. In this case, the width of the second and third step portions 209b and 209c becomes small. Consequently, the distances between the O-rings 214 that separate them and the distances between the pressure-sensitive hole 210, the valve port 211 and the inlet port 212 opening to the step portions 209a to 209c become short, too. The distances between the taper surfaces 216 inside the fitting hole 213 become short, as well. The requirement for machining accuracy of the pressure detecting passage 218 and the supply passage 201 that open to oppose the pressure-sensitive hole 210, the valve port 211 and the inlet port 212 on the inner peripheral surface of the fitting hole 213, becomes higher with the result that the production cost of the compressor becomes higher.
A predetermined open area must be secured, in some cases, in each of the supply passage 201 and the pressure detecting passage 218 in order to restrict an excessive pressure loss. In such a case, a part of each passage extends over the taper surface 216. When a part of the pressure detecting passage 218 or the supply passage 201 is open over the taper surface 216, the O-ring 214 is damaged when it passes over the taper surface 216 while being compressed, and a pressure leak is more likely to occur. In consequence, capacity control in the compressor becomes unstable.
If the inclination of the taper surface 216 is increased in order to avoid the possible damage of the O-ring 214, the problem that a part of the pressure detecting passage 218 and the supply passage 201 is open over the taper surface 216 can be avoided. However, because the O-ring 214 is drastically compressed, the resistance increases remarkably when the control valve 200 is inserted, and the assembling property of the control valve 200 to the compressor drops. In this case, too, the production cost of the compressor becomes higher.